Process and device for detecting the presence of an object, preferably a leaf sheet-shaped or sheet-shaped object for printing

ABSTRACT

Detecting the presence of an object, preferably a leaf sheet-shaped or sheet-shaped object on a transport path, especially for preparation and/or control of a processing of the object, preferably for printing the object in a printing machine, especially a digital printer, where the object is transported on the transport path past a sensor device, preferably a photoelectric barrier, for detection and registration of the front edge of the object in the transport direction. After detecting the front edge of the object and/or its entrance into the measurement area, it is checked at least once to determine whether the object continues to be present in the measurement area of the sensor device.

FIELD OF THE INVENTION

[0001] The invention involves a process and device for detecting the presence of an object, preferably a leaf sheet-shaped or sheet-shaped object on a transport path, especially for preparation and/or control of a processing of the object, preferably for printing the object in a printing machine, especially a digital printer, where the object is transported on the transport path past a sensor device, preferably a photoelectric barrier, for detection and registration of the front edge of the object in the transport direction.

BACKGROUND OF THE INVENTION

[0002] In the operation of a digital printer, in particular, during the operation of an electrophotographic printer, the imaging operation for printing must be prepared for each sheet to be printed, because a permanent printing block or mold is not used (non-impact printing). That is, the printed image must be recreated for each sheet to be printed, even if the printed image does not change from sheet to sheet. This imaging requires time so that the arrival of a new sheet must be announced at the proper time, so that time is available for the imaging and is planned for by the printer. The announcement of a next sheet is done by a sensor device which detects the presence and/or the arrival of an object on the transport path in its measurement area. This object can be the arriving sheet itself, which is detected by the sensor device as soon as its front edge enters the measurement area of the sensor device, but the object can also be a mark or the like, for example, which runs along with the conveyor belt and its presence is likewise detected by the sensor device as soon as the front edge enters the measurement area. In this process, primarily a one-way photoelectric barrier or a two-way photoelectric barrier, or a reflection photoelectric barrier, come into consideration as the sensor device.

[0003] One problem, however, can be that the sensor device should detect the entrance into its measurement area in as precise a manner as possible so that the measurement area of the sensor device, for example, through a narrow slit, is set to be as small as possible in order to, in this way, select the measurement inaccuracy that results from the extension of the measurement area itself, to be as small as possible. A precise sensor device of this type is namely also subject to slight interference effects by phenomena in the measurement area, which mediate the appearance of an existing object. For example, slightly extended, local damages, such as scratches or soiling, can also readily trigger the sensor device and in this way lead to erroneous triggerings or erroneous switchings of the imaging device of an electrophotographic printer.

SUMMARY OF THE INVENTION

[0004] The purpose of the invention is thus to improve a process and/or a sensor device to the effect that in spite of high precision, the danger of erroneous detection is reduced. This purpose is achieved in regard to the process in that after detecting the front edge of the object and/or its entrance into the measurement area, it is checked at least once to determine whether the object continues to be present in the measurement area of the sensor device. By this measure according to the invention, it can be reliably ensured that a more expansive object has actually entered into the measurement area of the sensor device and not a local position of interference that only gives the impression of an object.

[0005] According to another embodiment of the process according to the invention, the check is done multiply at defined intervals that can be relatively small, in that the sensor device operates by clock pulses. In this way, the entrance and exit of the object can be detected precisely and it can be recognized that in this entire detected area, only an extended object is present. In the process, the clock pulsing according to the invention can be time-referenced or path-referenced, whereby a timed frequent clock pulsing is allocated to corresponding path distances via another path measurement and can be converted into these path distances. However, different results and advantages result for the different clock pulsings. A timed clock pulsing can be implemented directly for the sensor device and is sufficient if the sensor device itself should make the decision about the presence of an object. If the clock pulsing is performed in a manner referenced to the path distance, the clock pulsing is only as uniform in time as the movement of the transport device used. However, this has the advantage for the direct preparation control, e.g. of an electrophotographic printer, that transport speed fluctuations no longer falsify the measurement result.

[0006] If the sensor device is clock-pulsed in a manner referenced to the path-distance or a time clock is otherwise set in relation to a path distance measurement, then a statement about the distance, for example, between the position of the sensor device and the print gap of the imaging device, can be made. This is especially true if, as provided according to a further embodiment, the position of the measurement area of the sensor device is defined and specified on the transport path with regard to a reference point. Also, as likewise preferably provided, the length of the object can be measured.

[0007] For the check of the presence of an object in the measurement area of the sensor device and to eliminate interference, a minimum length of an object to be expected is preferably provided, which is checked. For formatted objects, the shortest format length that should ever be used is taken into account for this purpose, whereby the prescribed minimum length is selected to be this short or for the purposes of safety, shorter. Each object that is shorter than the minimum length is considered to be a source of interference.

[0008] A device according to the invention is characterized in an independent solution of the inventive purpose, in that the sensor device is set up to check at least once whether the object is still present in its measurement area after the detection of the object. In particular, the device according to the invention for multiple checking for the presence of an object can be operated in a clock pulsed manner, namely clock pulsed in a time-referenced or path-distance-referenced manner. For a time-path relation, preferably the sensor device and a measurement device are connected together for measurement of a transport distance via a computational unit and/or a signal output unit. The position of the measurement area of the sensor device on the transport path of the objects is preferably defined and specified with regard to a reference point. For the transport of objects along the transport path, preferably a transparent conveyor belt is chosen, on which the objects can be placed and that itself does not interfere with an optically operating sensor device, unless it were to be soiled or scratched, for example, or otherwise damaged.

[0009] The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiment examples of a device according to the invention, from which other characteristics of the invention can also be gathered, but to which the invention is not limited in its scope, are shown schematically in the following drawings:

[0011]FIG. 1 which schematically shows a section of a paper transport path of a printer with a first embodiment form of a device according to the invention, depicted in the manner of a block diagram, in a side view, and

[0012]FIG. 2 which schematically shows a second embodiment form according to FIG. 1, with an additional path measurement device.

DETAILED DESCRIPTION OF THE INVENTION

[0013]FIG. 1 shows schematically in a side view and partially in the manner of a block diagram, a section of a transport path for the paper sheet to be printed by an electrophotographically operating printer having a sensor device for detecting a paper sheet on the transport path.

[0014] A transparent conveyor belt 1 is indicated, which runs along the transport path in the transport direction 2. On the conveyor belt 1, a paper sheet 3 is shown. Above the conveyor belt 1, a sensor device is located to detect a paper sheet 3 on the conveyor belt 1. The sensor device includes a photoelectric barrier 4 in particular, which registers the entrance and/or the presence of a paper sheet 3 in its measurement area and/or measurement point 5. The photoelectric barrier 4 is connected via a computational unit and output unit 6 with a time output device 7.

[0015] As soon as traveling the front edge of the paper sheet 3 traveling reaches the measurement point 5 of the photoelectric barrier 4 and enters into it, this is registered by the photoelectric barrier 4. This occurs because the photoelectric barrier 4, as a two-way photoelectric barrier whose light passes through the transparent conveyor belt 1 unobstructed, is suddenly interrupted, or because it registers, as a reflection light barrier, light reflected by the paper sheet 3. The presence of the paper sheet 3 in the area of the measurement point 5 is checked many times during its transport in a clock-pulsed manner with a clock-pulse from the time output device 7. After each repetition that has yielded the result that the paper sheet can still be detected at the measurement point 5, a counter of the computational and output unit 6 is incremented, so that the counting rate multiplied by the time interval of the clock pulses produces a measuring time period. This measuring time period corresponds, taking into account the transport speed of the paper sheet 3 in the transport direction 2, to a measuring distance 8 that the front edge of the paper sheet 3 passes through over the measuring time period, starting with the measuring point 5. This measuring distance 8 can have a defined minimum length, in order to ensure that a more expansive paper sheet 3 had actually been detected and that an interference or damage through a locally limited soiling or a scratch of the conveyor belt 1 is not present. For example, the measuring distance 8 can be selected to be somewhat shorter than the shortest expected paper sheet length of the paper sheet formats provided for use.

[0016] Because of the paper sheet 3 definitely recognized at the measuring point 5, the printer (not shown in greater detail) can be prepared for the arrival of the paper sheet in the print gap. The printing process, especially the imaging, can then be adjusted exactly in time to the arrival of the paper sheet. For this purpose, the position and/or the distance of the measuring point must be known as precisely as possible. This position is thus defined relative to a reference point 9. For the time preparation and adjustment of the printer, however, in addition to the position and/or distance of the measurement point 5 from the print gap, the measuring distance 8 must be taken into account. This is because only after this measuring distance 8 has passed, the paper sheet 3 is definitely recognized and is announced, so that this path distance up to arrival at the print gap is no longer available, and must be considered as a delay of the reporting of the paper sheet 3.

[0017] In FIG. 2, a second embodiment example of a device according to the invention is shown in a diagram corresponding to FIG. 1. The same structural elements are shown with the same reference indicators as shown in FIG. 1. In the embodiment example according to FIG. 2, only the time output device 7 of FIG. 1 has been replaced by a path measurement device 10, so that the clock pulsing and/or inquiry repetition through the photoelectric barrier 4 can occur in a manner having equal path sections. Also here, the measurement distance 8 is considered to be an already covered distance during the announcement of the paper sheet 3.

[0018] In both cases of FIG. 1 and 2, the photoelectric barrier 4 can be set so precisely and sharply defined that the measurement area and/or measuring point 5 is extended only a few micrometers. Interference by local foreign bodies or damage of the conveyor belt and resultant erroneous triggerings of the printer are prevented by the verifications over the measuring distance 8.

[0019] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 

What is claimed is:
 1. Process for detecting the presence of an object, preferably a leaf sheet-shaped or sheet-shaped object on a transport path, especially for preparation and/or control of a processing of the object, preferably for printing the object in a printing machine, especially a digital printer, where the object is transported on the transport path past a sensor device, preferably a photoelectric barrier, for detection and registration of the front edge of the object in the transport direction, characterized in that after detecting the front edge of the object, it is checked at least once to determine whether the object continues to be present in the measurement area of the sensor device.
 2. Process according to claim 1, characterized in that the check is done multiple times in a clock-pulsed manner.
 3. Process according to claim 2, characterized in that a certain time interval pulsing is specified.
 4. Process according to claim 2, characterized in that a transport distance covered by the object is measured and that a certain path section clock-pulsing is specified for the sensor device.
 5. Process according to claim 2, characterized in that the position of the measurement area of the sensor device is defined and specified on the transport path with regard to a reference point.
 6. Process according to claim 2, characterized in that for the check of the presence of the object, a minimum length of an object in the transport direction is taken into consideration, in such a way that only upon the presence of the object even after the minimum length has been covered in the measurement area past the sensor device, a detected object is recognized as such.
 7. Process according to claim 6, characterized in that when using formatted objects, the length of the smallest format provided for possible use is considered as a minimum length.
 8. Process according to claim 2, characterized in that the clock pulsing, when using a time interval clock pulsing taking into account the transport speed, is used for a measurement of the length of the object.
 9. Device for detecting the presence of an object, preferably a leaf sheet-shaped or sheet-shaped object on a transport path, especially for preparation and/or control of a processing of the object, preferably for printing the object in a printing machine, especially a digital printer, where the transport path passes by a sensor device, preferably a photoelectric barrier, for detection and registration of the front edge of the object in the transport direction, characterized in that the sensor device (4) is set up to check at least once to determine whether the object (3) continues to be present in the measurement area (5) after first detecting the object (3).
 10. Device according to claim 9, characterized in that the sensor device (4) is clock-pulsed for multiple checking.
 11. Device according to claim 10, characterized in that a certain time interval clock-pulsing is specified for the sensor device (4).
 12. Device according to claim 10, characterized by a measurement device (10) for measuring a transport path that is covered by the object (3) is in connection with the sensor device (4) to specify a certain path section clock-pulsing for the sensor device (4).
 13. Device according to claim 12, characterized in that the sensor device (4) and the measurement device (10) are connected to each other to measure the transport distance via a computational unit and/or a signal output unit (6).
 14. Device according to claim 9, characterized in that the position of the measurement area (5) of the sensor device (4) on the transport path is defined and specified with regard to a reference point (9).
 15. Device according to claim 9, characterized in that to transport the object (3) along the transport path, a transparent conveyor belt (1) is provided, on which the object (3) can be placed. 